In recent years, there have come into widespread use devices which handle image information as digital in order to perform highly effective information transmission and storage at that time, for example, compliant to formats such as MPEG or the like to compress the image by orthogonal transform such as discrete cosine transform or the like and motion compensation, both in broadcasting and general households.
In particular, MPEG2 (ISO/IEC 13818-2) is defined as a general-purpose image encoding format, and has widely been employed now by a broad range of applications for professional usage and for consumer usage. By employing the MPEG2 compression format, a code amount (bit rate) of 4 through 8 Mbps is allocated in the event of an interlaced scanning image of standard resolution having 720×480 pixels, for example, whereby high compression and good image quality can be realized. Also, a code amount (bit rate) of 18 through 22 Mbps is allocated in the event of an interlaced scanning image of high resolution having 1920×1088 pixels, whereby high compression and good image quality can be realized.
Also, standardization has been performed as Joint Model of Enhanced-Compression Video Coding which realizes higher encoding efficiency though greater computation amount is required for encoding and decoding thereof, and has become an international Standard called H.264 and MPEG-4 Part 10 (hereinafter written as “H.264/AVC (Advanced Video Coding)”).
With this MPEG and J.264/AVC, at the time of quantizing macroblocks, the size of quantization steps can be changed so that the compression rate is constant. Also, with MPEG, quantization parameters proportionate to the quantization steps are used, and with H.264/AVC, quantization parameters are used in which the parameter value increases by “6” when the quantization step doubles. In MPEG and H.264/AVC, quantization parameters are encoded (see PTL 1).